1. Field of the Invention
The present invention relates to a color liquid crystal display (LCD), and more particularly to a color LCD in which pixel electrodes of the same color located close to one another in a column direction are driven by a single data line.
2. Description of the Prior Art
Conventionally, an LCD having orientation control windows opened in a common electrode opposing pixel electrodes has been proposed in, for example, JPA H06-301036. An LCD having orientation control windows is a vertical orientation type LCD using liquid crystal having negative anisotropy of dielectric constant. The orientation of the liquid crystal is controlled by the curving of electric field caused between end portions of a pixel electrode and of an orientation control window. Accordingly, it is unnecessary to perform rubbing processing on orientation films to provide a pre-tilt angle.
3. Description of the Related Art
Liquid crystal located directly underneath an orientation control window is not subjected to any electric field and remains without being driven. The technique of placing a data line in such a region is proposed in Japanese Patent Application No. H10-337840 filed by the present applicant. An LCD having a data line overlapping an orientation window is described below. It is to be noted that this technique does not constitute the prior art of the present application.
FIG. 1 is a plan view showing a conventional LCD having a data line overlapping an orientation control window, and FIG. 2 shows a cross-sectional view taken along line Axe2x80x94A of FIG. 1. A plurality of gate lines 51 made of metal such as chromium are formed extending along a row direction on a transparent insulator substrate 50 composed of materials such as glass or quartz. Over this layer, although not shown in FIG. 2, thin-film transistors (TFT) 53 are formed for each pixel, and an interlayer insulating film 52 is formed covering the TFT. Over the interlayer isolation film 52, a plurality of data lines are formed extending in columns. A source region of a TFT 53 is connected to a data line 54. A portion of a gate line 51 constitutes a gate electrode of a TFT. A pixel electrode 56 is formed over the TFT with a planarization film 55 disposed in between. A drain region of the TFT is connected to the pixel electrode via a contact hole. A vertical orientation control film 57 is formed further on top. Provided on a substrate arranged opposing the substrate 50 are color filters 61 each colored with a primary color for image display. The primary color may be one of the three colors of red (R), green (G), and blue (B), or alternatively, cyan, magenta, and yellow. The following explanation is made using the three colors of RGB. A protective film 62 is provided over the color filters 61, and a common electrode 63 used commonly for all pixels and an orientation control film 64 are formed over the protective film 62. Orientation control windows 65 where no electrode is present are formed in the common electrode 63 in regions opposing pixel electrodes 56. Liquid crystal 70 is filled between these substrates 50,60. The orientation of liquid crystal molecules is controlled in accordance with the strength of electric field generated by a voltage applied between pixel electrodes 56 and the common electrode 63. In this way, the polarizing characteristic of the liquid crystal 70 is changed, controlling the transmittance of the light linearly polarized by the polarizers 41,42.
The liquid crystal 70 has negative anisotropy of dielectric constant. That is, the liquid crystal has the property of orienting itself in a direction perpendicular to the direction of the electric field. The orientation control films 57,64 are vertical orientation control films which may be made of organic materials such as polyimide and polyamide or of inorganic silane materials. Liquid crystal molecules are controlled by the orientation control films such that their initial orientation when no voltage is applied is in the direction along the line normal to the substrates. When an electric field along the length of the Figure is generated by applying a voltage between a pixel electrode 56 and the common electrode 63, the liquid crystal located between these electrodes are tilted in a direction perpendicular to the electric field, i.e., along the width of the Figure. At the end portions of the pixel electrode 56 and of the orientation control window 65, the electric field becomes curved, and the direction in which the liquid crystal molecules are tilted is accordingly controlled towards the orientation control window 65. No electric field is generated in a region directly underneath the orientation control window 65 because no voltage is applied. Liquid crystal molecules are therefore not tilted and remain without being driven in this region.
As shown in FIG. 1, the data line 54 is formed overlapping an orientation control window in each pixel. One data line 54 is connected to and overlapped on pixels of the same color. Specifically, a data line 54g driving green pixels overlaps green pixels indicated by G, a data line 54r driving red pixels overlaps red pixels indicated by R, and a data line 54b driving blue pixels overlaps blue pixels indicated by B.
The pixel electrodes 56 are arranged in a matrix, but the pixel electrodes in one column are shifted by half a pixel away from one, another in a row direction. In addition, pixels of the same color are not located adjacent to one another. This arrangement is the so-called delta arrangement. As a data line 54 drives pixels of the same color and overlaps those pixels of the same color in positions shifted by 1.5 pixels from one another, the data line is arranged meandering by an amplitude of 1.5 pixels.
FIG. 3 is a plan view of a liquid crystal display having orientation control windows 66 in the shape of two letter Y""s connected at their bottoms. Pixel electrodes indicated by rectangles are disposed in a delta arrangement. Each TFT 53 which includes a gate constituted by a portion of a gate line 51 extending along a row direction is formed for each pixel. The TFT is connected to the pixel electrode 56 via a contact hole. As the cross-section along Axe2x80x94A is identical to the cross-section of FIG. 2, the explanation will not be repeated.
The data line 54 is formed overlapping an orientation control window 65 in each pixel. One data line 54 is connected to and overlapped on pixels of the same color. Specifically, a data line 54g driving green pixels overlaps green pixels indicated by G, a data line 54r driving red pixels overlaps red pixels indicated by R, and a data line 54b driving blue pixels overlaps blue pixels indicated by B.
However, when a data line 54 is formed to overlap pixels that are shifted by 1.5 pixels as described above, the wiring of the data line 54 becomes long, possibly causing the following problems.
With the enlargement of an area in which the data line 54 and the common electrode 63 face one another, parasitic capacitance generated between the data line and the electrode becomes larger. Consequently, time required for applying a voltage to the data line 54 (referred to as the time constant) is increased. When the time constant is larger, it may not be possible to raise the voltage on the data line 54 within a predetermined time period. Accordingly, sufficient voltage may not be applied to the pixel electrodes 56, resulting in degradation of display quality.
As data lines 54 are made of metal such as chromium, a region in which a data line 54 is formed does not let light pass through. When this region is enlarged, the aperture ratio is reduced, causing a decrease in display contrast and therefore degradation of display quality.
By having data lines 54 meandering by an amplitude of 1.5 pixels, regions are created where two data lines 54 overlap. Margins must therefore be reserved to accommodate widths of the data lines and to maintain spaces between the data lines. This requires an increased amount of inter-pixel space and decreases aperture ratio.
In light of the above, the object of the present invention is to provide a LCD with high display quality in which the meandering amplitude of a data line is reduced, shortening the overall length of data lines.
According to the present invention conceived for accomplishing the above object, there is provided a color liquid crystal display comprising a plurality of pixel electrodes arranged in a matrix such that, in adjacent rows, positions of pixels associated with the same color are shifted from one another; and a data line extending in a column direction while overlapping predetermined pixel electrodes among said plurality of pixel electrodes, the data line electrically connecting to pixel electrodes associated with the same color and located closely along the column direction, while at least a portion of said data line overlaps pixel electrodes associated with a color different from the connected pixel electrodes.
In another aspect of the present invention, the arrangement of the pixel electrodes is a delta arrangement.
In a different aspect of the present invention, a row in which the data line overlaps a connected pixel electrode and an adjacent row in which the data line overlaps a pixel electrode of a different color are arranged alternately.
According to another aspect of the present invention, pixel electrodes on which the data line overlaps are only pixel electrodes of a different color located adjacent to the connected pixel electrodes.
According to a further aspect of the present invention, the color liquid crystal display comprises a common electrode provided opposing said plurality of pixel electrodes; liquid crystal sealed between said common electrode and said plurality of pixel electrodes; and an orientation controller for controlling an orientation of the liquid crystal. The liquid crystal has a negative anisotropy of dielectric constant.
As described above, at least a portion of the data line overlaps pixel electrodes of a different color according to the present invention. As a result, the length of the data line is shortened, and the meandering amplitude is made smaller. The time constant of the data line can therefore be reduced, achieving high display quality.
In the present invention, inter-pixel regions can be made smaller or pixels can be enlarged because the total area of data lines is reduced, and inter-pixel regions in which two data lines overlap no longer exist. Accordingly, the aperture ratio can be increased, accomplishing higher brightness and display quality.
In another aspect of the present invention, the orientation controller comprises orientation control windows including electrode openings made in the common electrode at positions corresponding to the plurality of pixel electrodes.
According to a different aspect of the present invention, the orientation controller comprises orientation control slopes disposed on one or both of an interface between the common electrode and the liquid crystal, and interfaces between the plurality of electrodes facing the liquid crystal, the orientation control slopes formed by causing the facing interfaces to protrude towards the liquid crystal.
According to a further aspect of the present invention, the orientation controller is provided within pixel regions corresponding to each of the plurality of pixel electrodes, and functions as an orientation divider for providing a plurality of discrete orientations of liquid crystal within each pixel region. According to this aspect, the data line overlaps the orientation controllers within predetermined pixel regions.
As described above, a predetermined data line overlaps an orientation controller. When liquid crystal with negative anisotropy of dielectric constant is employed in a vertical orientation type LCD, the orientation of the liquid crystal constantly remains unchanged from the vertical direction within regions directly above an orientation control window or an orientation control slope explained later. Such regions therefore do not contribute when displaying images. Accordingly, no decrease in aperture ratio of the overall display is caused by overlapping data lines on these regions. As no electric fields are applied to liquid crystal located directly above such orientation controller, light leakage may possibly occur when the orientation of liquid crystal in these regions is altered by other factors. However, in the present invention, while the length of data line wiring is minimized, the data lines may be formed of light-shielding materials and arranged to overlap these orientation control means, thereby also facilitating prevention of light leakage.
In a further different aspect of the present invention, a transistor is connected to each of the plurality of pixel electrodes, and the data line is connected via the transistors to the pixel electrodes, among the plurality of pixel electrodes, that are associated with the same color and located closely along the column direction.
The data line is arranged to overlap either a connected pixel electrode or a pixel electrode of a different color located adjacent thereof. Accordingly, even when the data line overlaps pixel electrodes of a color different from the associated color, the wiring between the transistor for a connected pixel electrode and the data line does not need to be made much longer and is kept to a minimal length. Operational deficiencies due to long wiring to transistors can therefore be avoided, and transistors can be reliably operated at a high speed to supply data to be displayed in each pixel from the data line to pixel electrodes via the transistors.